Storm Coming Together Off Coast of California, Expected to Strike by Middle of the Week

Posted: December 19, 2023 4:10 pm

A storm is brewing in the Pacific Ocean, threatening to bring heavy rain to Southern California and into the Desert Southwest. The weather maker will bring the biggest blast of moisture that the region has seen since what was left of Hurricane Hilary spun up over Southern California in August.

First Major Storm of the Season Bears Down on Southern California

California is bracing for what is anticipated to be the first big storm event of the season. The storm could complicate travel heading into the holiday weekend for much of the West. The upcoming weather event will bring the most significant moisture since Hurricane Hilary dropped widespread rainfall amounts of 1 to 3 inches across Southern California and beyond on August 20 and 21.

While Hilary was a whopper of a storm, most portions of Southern California have only picked up minuscule amounts of rain since then. For instance, the official rain gauge in downtown Los Angeles has only recorded 0.41 of an inch since Hilary exited the city. This gauge typically picks up an average of 2.50 inches over this same time period, speaking to the abnormally dry conditions as of late.

Timing and Intensity of Incoming Rain

The moisture will begin to arrive in the southern part of the Golden State starting on Wednesday and lingering through Friday. The current forecast models are calling for downtown Los Angeles to pick up 2 inches of rain out of this system. The heaviest precipitation will fall along the west and southwest-facing slopes of the Coast Ranges, expected to pick up rainfall amounts of up to 6 inches.

The intermittent rain and drizzle will also be an issue for the northern and central portions of the state through the middle of the week thanks to a prior storm system that came in from the Pacific a few days ago. This storm will eventually move off the coast just as the second system arrives into cities such as San Luis Obispo and Santa Barbara on Wednesday.

Los Angeles is likely to experience the heaviest rain on Thursday. San Diego will see the potent rain bands late Thursday and into Friday. Slick roads and the chance of flooding will be a concern in this region.

Temperatures will remain atypically warm across Donner Pass on Interstate 80, keeping the moisture falling mostly as rain or a wet snow. The same mass of warm air associated with this storm will also mitigate the odds of snow for Tejon and Cajon passes in the southern part of the state. Despite the lack of snow, dense fog and strong winds could present problems for motorists along portions of interstates 5, 8, and 15 by the last part of the week.

What Can the Desert Southwest Expect to See?

The weather event will continue to track inland on Friday and Saturday. This movement will bring the chance of rain to the Desert Southwest, including southern Nevada and the bulk of Arizona. This forecast is good news for drought-stricken Arizona.

Phoenix also experienced an exceptionally dry fall with only 0.45 inches of rain on the record books since September 1. This compares to the historical average of just over 2 inches for the fall months. The Phoenix metropolitan area could see up to an inch of rain out of this one system.

It has been a different situation for Las Vegas, a part of the desert that has seen about 1.5 times the usual amount of rain for this time of the year. Sin City has recorded 1.72 inches of rain since the beginning of September, compared to the norm of 1.15 inches. The incoming storm could deliver up to an inch of rain.

Moving to the Pacific Northwest

The Pacific Northwest will enjoy mostly dry conditions through Thursday before a different storm system comes into the region from the northern Pacific Ocean, bringing colder air and moisture along with it. The snow levels will fall across the passes in Washington State and Oregon on Friday night while a chilly rain will be the story for the Interstate 5 corridor between Seattle and Portland.

The precipitation from the storm coming into the Northeast will meet with what is left of the system that hit Southern California earlier in the week to create the good odds of low-elevation rain and snow in the higher terrains of the interior West. This merger of moisture could trigger travel complications for the holiday weekend.

Forecasters are predicting that this week’s stormy weather across Southern California could be a harbinger of things to come as El Niño kicks into high gear. However, El Niño is known for being unpredictable, meaning that residents cannot count on another winter with above-average rainfall this year. Only time will tell how much of an influence El Niño will have on the weather patterns on the West Coast.

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